The present invention relates to a method and to apparatus for manipulating sheets in paper processing plants or the like, especially for manipulating layers or stacks of paper sheets on their way to a packing machine. More particularly, the invention relates to improvements in apparatus for transporting layers or stacks of sheets to a packing or other processing machine in such a way that fluctuations in the rate of delivery of stacks to the apparatus are compensated for before the stacks reach the processing machine so that the rate of admission of stacks into the processing machine invariably conforms to the operating speed of the processing machine and the apparatus compensates for eventual pronounced or less pronounced fluctuations of the rate of admission of stacks thereto, for example, as a result of intermittent delivery of groups of stacks and/or as a result of segregation of unsatisfactory stacks from the remaining stacks.
It is already known to intermittently deliver groups of abutting or closely adjacent stacks to a station which is disposed between the stack forming unit and the processing machine, and to thereupon singularize the stacks of such groups so as to ensure that the processing machine receives properly spaced-apart stacks at a desired rate, namely at a rate conforming to the momentary requirements of the processing machine. To this end, a first conveyor receives groups of stacks from a second conveyor at regular or irregular intervals and is designed to ensure that one outermost stack of the freshly delivered group is moved into abutment with one outermost stack of the previously delivered group. Thus, the first conveyor invariably supports a series of abutting stacks and cooperates with a third (singularizing) conveyor which removes or receives from the first conveyor discrete stacks at the rate which conforms to the then prevailing speed of the processing machine. Reference may be had to the commonly owned copending patent application Ser. No. 374,939 filed May 5, 1982 by Aykut et al., now U.S. Pat. No. 4,518,075 granted May 21, 1985.
U.S. Pat. No. 4,230,218 discloses a modified apparatus for transporting stacks of paper sheets or the like wherein a belt conveyor is driven at a constant speed and cooperates with a belt run having upper and lower belts which are disposed in front of and partially overlap the belt conveyor. The belt run is driven intermittently at a speed varying between zero and a speed exceeding the constant speed of the belt conveyor. The upper and lower belts of the belt run clamp the stacks of paper sheets therebetween and advance the clamped stacks at an elevated speed so as to move the foremost stack into abutment with the last stack on the belt conveyor. The latter cooperates with a singularizing conveyor which converts the group of abutting stacks into a series of discrete stacks advancing toward a packing or other processing machine. The mutual spacing of singularized stacks corresponds to (i.e., it is a function of) the operating speed of the processing machine.
The apparatus of the aforementioned copending application Ser. No. 374,939 deviates from the patented apparatus because it comprises an intermittently driven transverse conveyor preceding a continuously driven gathering conveyor which is followed by the singularizing conveyor. The gathering conveyor comprises several discrete endless bands which are disposed one after the other, as considered in the direction of transport of stacks toward the singularizing conveyor. Each discrete band can be accelerated individually from a lower basic speed to a higher speed so as to ensure that the trailing stack or stacks can be moved nearer to the preceding stacks ahead of the singularizing conveyor. This ensures that the gathering conveyor can accumulate a group of abutting stacks, the foremost one of which advances into the range of the singularizing conveyor whose operation is synchronized with that of the processing machine. In other words, the bands of the gathering conveyor cooperate to compensate for eventual irregularities in the rate of delivery of stacks by the transverse conveyor in order to enable the singularizing conveyor to invariably establish gaps of desired width between the series of discrete stacks.
The aforediscussed apparatus operate satisfactorily under normal circumstances, i.e., the processing machine (normally a packing machine) can receive discrete stacks at a desired rate which enables it to perform the desired operations even if the operating speed varies for any one of a variety of reasons. However, such apparatus cannot ensure predictable delivery of stacks or analogous accumulations of paper sheets or the like to a processing machine if certain stacks must be segregated from other stacks because they exhibit defects or for any other reason. This creates pronounced gaps in the stream of stacks which are delivered to the gathering conveyor so that it would be necessary to effect extremely high acceleration of discrete bands forming part of the gathering conveyor with attendant danger of deformation of the stacks. Alternatively, the path along which the stacks following one or more segregated stacks must be advanced at a higher than average speed is much longer than practical or warranted in a production line for the packing of reams of paper sheets or for the making of steno pads, exercise books and analogous stationery products. In the absence of such undertakings, the processing machine cannot receive stacks at a desired rate; this can cause damage to the processing machine (for example, a packing machine) and/or destruction of stacks which are delivered to the processing machine at inopportune times.
In accordance with another prior proposal which is disclosed in German Offenlegungsschrift No. 27 40 175, the speed of the motor which drives the packing machine is regulated so as to account for the absence of regular or predictable delivery of commodities (biscuits or the like) thereto. This is not a satisfactory solution in production lines which turn out large numbers of packed or otherwise processed goods per unit of time. First of all, repeated acceleration and deceleration of all moving parts in a packing machine for reams of paper sheets or the like entails pronounced wear and greatly reduces the useful life of such machines. Moreover, the stresses upon repeatedly accelerated and decelerated parts are so pronounced that they cannot be accepted in production lines for the making of stationery products or the like which are turned out at the presently required rates.
OBJECTS AND SUMMARY OF THE INVENTION
An object of the invention is to provide a novel and improved apparatus for manipulating stacks or analogous accumulations of paper sheets or the like between a stack forming and a stack processing machine.
Another object of the invention is to provide an apparatus which can deliver commodities to a processing machine at an optimum rate irrespective of fluctuations in the operating speed of the processing machine and/or fluctuations in the rate of delivery of commodities to the unit or units which, in turn, deliver commodities to the processing machine.
A further object of the invention is to provide a novel and improved method of manipulating stacks of paper sheets between a sheet cutter and a packing machine.
An additional object of the invention is to provide a relatively simple and compact apparatus which can fully compensate for intermittent and randomly or regularly recurring deviations of the rate of delivery of commodities thereto as a result of segregation of unsatisfactory commodities or for any other reason.
Still another object of the invention is to provide the apparatus with novel and improved means for regulating the speed of its conveyors.
An additional object of the invention is to provide an apparatus which can be installed in existing production lines as a superior substitute for heretofore known stack gathering and singularizing apparatus.
Another object of the invention is to provide a novel and improved control system for use in conjunction with or for incorporation in the above outlined apparatus.
One feature of the invention resides in the provision of an apparatus for delivering discrete commodities to a processing machine, particularly for delivering spaced-apart stacks of paper sheets to a packing machine. The apparatus comprises a first conveyor (e.g., an endless belt or chain conveyor) which serves to receive groups of commodities at regular or irregular intervals, which must be brought to a standstill whenever it is to receive a fresh group of commodities and which can advance the commodities in a predetermined direction, a gathering conveyor having a plurality of individual conveyors (e.g., discrete endless belt or chain conveyors) serving to accumulate the groups of commodities into a row of closely adjacent commodities by moving the commodities in the aforementioned direction, a singularizing conveyor (which can also include a series of endless belt or chain conveyors) which serves to subdivide the row into a series of spaced-apart commodities, first prime mover means for driving the individual conveyors of the gathering conveyor at a preferably (but not necessarily) constant first speed, variable-speed second prime mover means (e.g., a variable-speed electric motor) which is operable to drive the first conveyor at a plurality of speeds including at least one speed higher than the first speed, clutches or other suitable means for selectively or jointly coupling the individual conveyors of the gathering conveyor to the second prime mover means so that the latter can drive the individual conveyors at a speed exceeding the first speed, first or master encoder means connected with the first prime mover means and serving to generate first signals at a frequency which is proportional to the first speed, second or slave encoder means connected with the second prime mover means and serving to generate second signals at a frequency which is proportional to the speed of the first conveyor, a source of reference signals (e.g., a signal comparing stage) connected with the first and second encoder means and serving to transmit to the second prime mover means operating signals which are indicative of the relationship between the frequencies of the first and second signals, and means for influencing the operating signals in addition to the first and second signals. Such influencing means comprises first and second signal counter means connected with the first encoder means as well as with the source of reference signals and respectively arranged to store first signals on stoppage of the second prime mover means for the purpose of allowing for delivery of a fresh group of commodities to the first conveyor and as a result of segregation of commodities from one or more groups ahead of the first conveyor. Thus, the first counter means is designed to influence the operating signals for the purpose of compensating for interruptions of movement of the first conveyor whenever the latter is to receive a fresh group of commodities, and the second counter means is designed to influence the operating signals for the purpose of compensating for (often long-lasting) interruptions in regular delivery of groups to the first conveyor, for example, as a result of removal of samples from the path along which the commodities move toward the first conveyor, as a result of segregation of one or more defective commodities from such path, or for any other reason which could interfere with the formation of a continuous row of commodities on the gathering conveyor and with proper singularization of commodities by the singularizing conveyor.
The apparatus can further comprise third counter means which is connected with the first encoder means and serves to transmit to the second counter means an output signal in response to reception of a predetermined number of first signals denoting the format of the commodities. The second counter means is then arranged to reduce the number of signals which are stored therein (e.g., to expel some signals) in response to each output signal from the third counter means. A memory can be connected with the second counter means to temporarily store the signals which are expelled from the second counter means in response to reception of an output signal from the third counter means.
The apparatus further comprises a main control unit which controls the operation of the processing machine and, if necessary, the operation of one or more additional machines in a production line including the processing machine. Such control unit can serve to transmit a signal which activates (starts) the first counter means in response to stoppage of the second prime mover means for the purpose of delivery thereto of a fresh group of commodities, and a signal which activates (starts) the second counter means in response to each start of segregation of commodities from their path leading to the first conveyor.
First and second transmissions are respectively interposed between the first and second prime mover means on the one hand and the input elements of the first and second encoder means on the other hand. The first encoder means is preferably arranged to transmit a first signal whenever the individual conveyors cover a unit distance while receiving motion from the first or second prime mover means, and the second encoder means is preferably arranged to transmit a second signal whenever the first conveyor covers such unit distance while receiving motion from the second prime mover means.
The first conveyor can comprise an endless belt or chain conveyor, each individual conveyor of the gathering conveyor can constitute an endless belt or chain conveyor, and each individual conveyor of the singularizing conveyor can constitute an endless belt or chain conveyor.
The apparatus can further comprise a signal emitter which can transmit a signal to the first counter means independently of first signals which are being transmitted by the first encoder means, and another signal emitter can be connected with the second counter means, e.g., to transmit signals denoting the selected or desired format of the commodities.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved apparatus itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.